Thermosetting coating compositions usually contain a hydroxyl or epoxy-containing component and a cross-linking component; curing catalysts are often added to reduce curing time and/or temperature. Curing times of up to 1/2 hour and curing temperatures of up to 200.degree. C. are for many purposes acceptable in the thermosetting coating field.
The cross-linking component reacts during stoving with hydroxyl and/or epoxy groups of the main binder component, and the cross-linking provides a coating which is insoluble and infusible, and therefore resistant to solvents and elevated temperatures.
Another type of coating materials contains an air-drying binder, which can cross-link through carbon-carbon double bonds, in contact with oxygen; drying accelerators are here some metal compounds, such as Co- and Mn-naphthenate.
U.S. Pat. No. 4,332,711, issued June 1, 1982 discloses a thermosetting binder composition comprising:
(I) a mixture or precondensate of PA0 (II) as curing catalyst a transesterification-promoting metal salt or metal complex which is soluble in liquid hydro carbons.
(1) a non-acidic resinous compound essentially free of ethylenical unsaturation, having a molecular weight of at least 900 and a hydroxyl content of at least 0.2 equivalents per 100 g, and PA1 (2) as cross-linking agent a non-acidic polyester of a polycarboxylic acid, having more than one beta-hydroxyl ester group per molecule, at least one of components (1) and (2) having a hydroxyl functionality of more than 2, and PA1 (1) a non-acidic resinous compound essentially free of ethylenical unsaturation, having a molecular weight of at least 900 and a hydroxyl content of at least 0.2 equivalent per 100 g, and PA1 (2) as cross-linking agent a non-acidic polyester of a polycarboxylic acid having more than one beta-hydroxyl ester group per molecule, at least one of components (1) and (2) having a hydroxyl or beta-hydroxyl ester functionality, respectively, of more than 2,
U.S. patent application Ser. No. 255,196, filed Apr. 20, 1981, now U.S. Pat. No. 4,362,847, issued Dec. 7, 1982, describes similar compositions, in which the transesterification-promoting metal compound (II) is insoluble in liquid hydrocarbons.
Such curing systems operate by transesterification of the ester groups of the cross-linking agent with hydroxyl groups of the resinous compound, with elimination of a glycol.
According to the prior applications, the glycol part of component (I) (2) may have substituents such as alkyl-, ether- or stable ester groups, such as those derived from branched mono-carboxylic acids. It has been demonstrated that this ester group does not generally react.